The present disclosure relates to a control device and a control method for a fuel pump.
An internal combustion engine disclosed in US Patent Application Publication No. 2009/0217910 includes a fuel injection valve for injecting fuel into a cylinder, a fuel pipe connected to the fuel injection valve, and a fuel pump for supplying the fuel to the fuel pipe. The fuel pump includes a plunger disposed in the cylinder. The plunger is made of a magnetic material. The plunger is constantly biased in a first direction by a biasing spring provided in the fuel pump. The fuel pump includes a coil for exciting the plunger. When the coil is energized, the plunger is excited by a magnetic field generated around the coil. When the plunger is energized, the plunger moves in a second direction opposite to the first direction against the biasing force of the biasing spring. When energization to the coil is stopped, excitation of the plunger is cancelled and the plunger moves in the first direction according to the biasing force of the biasing spring. In this manner, in the fuel pump, the plunger reciprocates in the cylinder. Each time the plunger reciprocates, the fuel pump executes a suction operation for drawing in fuel and a discharge operation for pressurizing and discharging the drawn fuel.
In the control device of the fuel pump described in the above publication, when the fuel injection amount from the fuel injection valve is within a predetermined range, the driving cycle of the fuel injection valve and the driving cycle of the fuel pump are set to be the same. Therefore, one fuel discharge from the fuel pump is performed in response to one fuel injection from the fuel injection valve. With this configuration, in order to allow a sufficient amount of fuel to be supplied to the fuel pipe with respect to the fuel injection amount from the fuel injection valve, it is necessary to design the fuel pump so that the maximum amount of fuel that can be discharged from the fuel pump is increased.
On the other hand, there is a demand for downsizing the fuel pump as downsizing of the internal combustion engine is desired. However, with a small-sized fuel pump, the maximum amount of fuel that can be discharged from the fuel pump at one time is small. Accordingly, when the control device described in the above publication is adapted for such a small-sized fuel pump, the amount of fuel discharged from the fuel pump at one time is insufficient for one fuel injection amount from the fuel injection valve, which may not be able to supply a sufficient amount of fuel to the fuel pipe. Therefore, there is room for improving the controllability of the fuel pressure in the fuel pipe.